I don't see enough data in either story presented (average speed is higher leading to more fatalities vs. isolation/disruption) to come to a reliable conclusion

I don't see enough data in either story presented (average speed is higher leading to more fatalities vs. isolation/disruption) to come to a reliable conclusion. It's clear enough that higher speeds lead to crashes being more likely fatal on average, but a key part of the argument is acknowledging that there are much fewer cars on the road - which would tend to reduce the number of crashes. You would have to look at the data to see which factor dominates.